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(New) Simple Question about unusual current!

  1. Oct 21, 2013 #1
    My first post on the forums, go easy on me...

    So I'm getting a feel for the new lab my college has and all of the equipment in it so I thought I'd set up some VERY simple circuits just to get used to some of the DC power sources (there are a few different ones).

    No matter what I do though, the current always seems to be slightly HIGHER than the expected value coming from the given voltage and resistance.

    For example: I'll set up V = 10v R = 10Ω and get values above the expected (slightly)
    I'll hit 1 amp @ 9.8 volts
    I hit 1.1 amps @ 10.75 volts
    I hit 1.2 amps at 11.7 volts

    Any idea what seems to be causing this simulated lower resistance?
  2. jcsd
  3. Oct 21, 2013 #2


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    Staff: Mentor

    Including measuring the same setup with a different voltmeter and ammeter? And trying different 10 ohm resistors?
  4. Oct 22, 2013 #3


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    Gold Member

    A 9.8 ohm resistor? Obviously the voltage, current, or resistance measurements are incorrect, or any combination of the three. Not that I'm really telling you anything you don't already know. :) Are there any lab standards, recently calibrated supplies or meters, 1% or 0.1% resistors. Is your lab near the Mystery Spot in Santa Cruz California?
  5. Oct 22, 2013 #4


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    Gold Member

    driedupsharpie, Welcome to Physics Forums!

    Both Nugatory and meBigGuy have offered good suggestions to explain your unexpected readings. My suggestion is this: When just starting out in electronics place your trust...all your trust...in Ohm's Law! It has held true in every single test ever performed with it so far. So, there is some inaccuracy in your setup: either the current reading, the voltage reading, or the resistance value is faulty. One of these is giving you "unexpected results".

    Now, once you discover that Ohm's Law is reliable, you may continue onward to more complex circuits knowing that the fundamentals are totally under control. This is the foundation you rest on while ascending the complexity ladder of electronics.

    Cheers, Bobbywhy
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